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<!--
javascript 实现
ECMAScript 标准

ECMAScript 5

ES6 / 7 / 8

ECMAScript 6 === ECMAScript 2015
ECMAScript 2016
ECMAScript 2017
...
ECMAScript 2021


Babel: es6 语法 -> es5 语法
Polyfill: es6 api -> es5 api

let, const, () => {}
var, function() {}
Promise API
const app = require("module")
-->

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